GPS has no compass heading information, actually. This is why your
GPS doesn't know which way to point the "heading up" display on the
chart plotter when the boat is stopped, unless you have a compass
sensor input.

The heading information on a GPS-only system depends on measuring the
change in the lat/long over several measuring periods before it
displays heading information. If the boat merely rotates around its
anchor, this information will not be available or will be totally
inaccurate.

GPS receivers only provide 3 pieces of information. Latitude,
Longitude and Altitude....the 3 dimensions in space. All other
information (speed, heading, COG, VMG, etc.) are all derived by the
computer monitoring the changes in these 3 dimensions over
time.....many seconds. That's why it takes so long for it to change
heading or speed or VMG or other derived outputs when you make that
turn or come about.



On Mon, 26 Jan 2004 21:12:28 -0500, "wg992000"
wrote:

Does anyone know if there is a set relationship between the accuracy / DOP/
Differenctial indicated on the GPS page to the accuracy of the compass
direction? ( of the GPS)

ie. Trying to determine how far off the compass rose would be off if WAAS
sat's were being received and there was high accuracy.

Kind of new at this. Any thoughts appreciated.



Larry W4CSC

Is it just me or did the US and UK just capture 1/3
of the world's sweetest oil supply? What idiot wants to
GIVE IT BACK?!!